• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.2
• /
• pp.58.2-58.2
• /
• 2018

Theoretically, the magnetic helicity transport flux through the solar surface into the upper atmosphere can be estimated indefinitely precisely by magnetic field footpoint tracking if the observational resolution is infinitely fine, even with magnetic flux emergence or submergence. In reality, the temporal and spatial resolutions of observations are limited. When magnetic flux emerging or submerging, the footpoint velocity goes to infinity and the normal magnetic field vanishes at the polarity inversion line. A finite observational resolution thus generates a blackout area in helicity flux estimation near the polarity inversion line. It is questioned how much magnetic helicity is underestimated with a footpoint tracking method due to the absence of information in the blackout area. We adopt the analytical models of Gold-Hoyle and Lundquist force-free flux ropes and let them emerging from below the solar surface. The observation and the helicity integration can start at different emerging stages of the flux rope, i.e., the photospheric plane initially cuts the flux rope at different levels. We calculate the magnetic helicity of the flux rope below the photospheric level, which is eventually to emerge, except the helicity hidden in the region to be swept by the blackout area with different widths. Our calculation suggests that the error in the integrated helicity flux estimate is about half of the real value or even larger when small scale magnetic structures emerge into the solar atmosphere.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.69.1-69.1
• /
• 2019

A series of numerical MHD simulations are performed to investigate the evolution of coronal magnetic fields consisting of two flux ropes and an overlying field. Depending on the directions of the axial current and the axial field, two co-helicity cases and two counter-helicity cases are addressed. In Case 1, in which both the axial currents and the axial fields are parallel, flux rope merging bears a huge flux rope with a large winding number. This flux rope naturally erupts, but the whole evolutionary process is rather slow. In Case 2, in which the axial currents are parallel while the axial fields are antiparallel, a self-closed structure is formed and it drives eruption. In Case 3, in which the axial currents are antiparallel and the axial fields are parallel, each flux rope erupts independently and the presence of the other flux rope does not affect the eruption of one flux rope. In Case 4, in which both the axial currents and the axial fields are antiparallel, interaction of the flux ropes and the overlying field effects a breakout reconnection creating an apple-like CME configuration. Our study tells what kind of eruption mechanisms are involved for different eruption features observed.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.4
• /
• pp.417-423
• /
• 2015

In this study, Magnetic Flux Leakage(MFL)-based inspection system was applied to detect the local fault of wire rope. To verify the feasibility of the proposed damage detection technique, an 4-channel MFL sensor head prototype was designed and fabricated. A wire rope with several types of cross-sectional damages were fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the wire rope specimen. To interpret the condition of the wire rope, magnetic flux signals were used to determine the locations of the flaws. To improve the resolution of signal, the instantaneous variation value of magnetic flux was utilized. Measured signals from the damaged specimen were compared with thresholds set for objective decision making. Finally, the results were compared with information on actual inflicted damages to confirm the accuracy and effectiveness of the proposed cable monitoring method.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.89.2-89.2
• /
• 2011

The geometry of an MC (magnetic cloud) in the interplanetary space can be estimated by the magnetic flux rope model. But the single point observation in the interplanetary space near the Earth is scanty to comprehend the global configuration of MC because the MC is considered a huge loop extending from the Sun with both legs rooted on the Sun. If the MC is observed at two different locations sufficiently far away from each other, it may provide the global configuration of the MC. In this study, we model the MC which is observed two different locations using a simple straight cylinder model. The MC model fit parameters are the flux rope axis orientation (${\Theta}$, ${\phi}$), the intensity of the magnetic field at the flux rope axis ($B_0$), the radius of the MC ($R_0$), and the impact parameter (p), etc. With the MC model fit parameters we look into the difference between two observed MC geometries and also calculate the magnetic flux and helicity of the MC.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.63.2-63.2
• /
• 2015

Solar flare is one of the energetic phenomena observed on the Sun, and it is often accompanied with eruptions such as global-scale eruption of a flux rope (filament/prominence eruption) and small-scale eruption of a plasmoid. A flare itself is a dissipative phenomenon where accumulated electric current representing free magnetic energy is dissipated quickly at a special location called a current sheet formed in a generally highly conductive solar corona. Previous studies have demonstrated how a solar magnetic field placed on the Sun forms a current sheet when magnetic shear is added to the field. Our study is focused on a self-consistent process of how a subsurface magnetic field emerges into the solar atmosphere and forms a current sheet in the corona. This study also gives light to a relation among a flare and two types of flare-associated eruptions; flux-rope eruption and plasmoid eruption.

• 제어로봇시스템학회:학술대회논문집
• /
• 2002.10a
• /
• pp.79.5-79
• /
• 2002

$\textbullet$ Introduction $\textbullet$ Deterioration of wire rope $\textbullet$ Magnetic flux leakage Instrument $\textbullet$ Experiment setup $\textbullet$ Performance of the instrument $\textbullet$ Conclusions

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.2
• /
• pp.45.2-45.2
• /
• 2018

Twisted magnetic flux tubes (also called magnetic flux ropes) are believed to play a crucial role in solar eruptive phenomena. The evolution of a single flux rope with or without the influence of an overlying field of a simple geometry has been extensively studied and its physics is rather well understood. Observations show that interacting flux tubes are often involved in solar eruptions. It was Lau and Finn (1996) who intensively studied the interaction between two flux ropes, whose footpoints are anchored in two parallel planes. In this too simplified setting, the curvature of the flux rope axial fields is totally ignored. In our study, the footpoints of flux ropes are placed in a single plane containing a polarity inversion line as in the real solar active region. Our simulation study is performed for four cases: (1) co-axial field and co-axial current (co-helicity), (2) counter-axial field and co-axial current (counter-helicity), (3) co-axial field and counter-axial current (counter-helicity), and (4) counter-axial field and counter-axial current (co-helicity). Except case 3, each case is found to be related with certain eruptive features.

• The Bulletin of The Korean Astronomical Society
• /
• v.40 no.1
• /
• pp.66.3-67
• /
• 2015

Without scrutinizing reflection, the plasma comprising a coronal loop is usually regarded to reside within a flux rope. This picture seems to have been adopted from laboratory plasma pinches, in which a plasma of high density and pressure is confined in the vicinity of the flux rope axis by magnetic tension and magnetic pressure of the concave inward magnetic field. Such a configuration, in which the plasma pressure gradient and the field line curvature vector are almost parallel, however, is known to be vulnerable to ballooning instabilities (to which belong interchange instabilities as a subset). In coronal loops, however, ideal MHD (magnetohydrodynamic) ballooning instabilities are impeded by a very small field line curvature and the line-tying condition. We, therefore, focus on non-ideal (resistive) effects in this study. The footpoints of coronal loops are constantly under random motions of convective scales, which twist individual loop strands quite randomly. The loop strands with the axial current of the same direction tend to coalesce by magnetic reconnection. In this reconnection process, the plasma in the loop system is redistributed in such a way that a smaller potential energy of the system is attained. We have performed numerical MHD simulations to investigate the plasma redistribution in coalescence of many small flux ropes. Our results clearly show that the redistributed plasma is more accumulated between flux ropes rather than near the magnetic axes of flux ropes. The Joule heating, however, creates a different temperature distribution than the density distribution. Our study may give a hint of which part of magnetic field we are looking to in an observation.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.71.1-71.1
• /
• 2019

The solar magnetic field comes from the solar interior and is related to various phenomena on the Sun. To understand this process, many studies have been conducted to produce its evolution using a single flux rope. In this study, we are interested in the emergence of two flux ropes and their evolution, which takes longer than the emergence of a single flux rope. To construct it, we develop a flux emergence simulation by applying a parallel computing to reduce a computation time in a wider domain. The original simulation code had been written in Fortran 77. We modify it to a version of Fortran 90 with Message Passing Interface (MPI). The results of the original and new simulation are compared on the NEC SX-Aurora TSUBASA which is a vector engine processor. The parallelized version is faster than running on a single core and it shows a possibility to handle large amounts of calculation. Based on this model, we can construct a complex flux emergence system, such as an evolution of two magnetic flux ropes.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.54.1-54.1
• /
• 2019

Solar observations often show that interaction of more than one flux rope is involved in solar eruptions. In this regard, Lau and Finn (1996) intensively studied the interaction of two flux ropes, which reside in between two parallel planes each mimicking one polarity region of the solar photosphere. However, this geometry is quite far from the real solar situation, in which all feet of flux tubes are rooted in one surface only. In this paper, we study the interaction of two flux ropes in a semi-infinite region above a plane representing the solar photosphere. Four cases of the flux rope interaction are investigated in our MHD simulation study: (1) parallel axial fields and parallel axial currents (co-helicity), (2) antiparallel axial fields and parallel axial currents (counter-helicity), (3) parallel axial fields and antiparallel axial currents (counter-helicity), and (4) antiparallel axial fields and antiparallel axial currents (co-helicity). Each case consists of four or six subcases according to the background field direction relative to the flux ropes and the relative positions of the flux rope footpoints. In our simulations, all the cases eventually show eruptive behaviors, but their degree of explosiveness and field topological evolutions are quite different. We construct artificial emission measure maps based on the simulations and compare them with images of CME observations, which provides us with information on what field configurations may generate certain eruption features.